Assembly of immunoglobulin chains was studied in SAMM 368, a transplantable myeloma of mice. Tissue culture clones of this tumor, shown to contain 2 myeloma proteins, an IgA and an IgG2b, as well as variant clones, producing only a single myeloma protein were examined. No evidence of intracellular or extracellular mixing of IgG and IgA was found. Over 50 lymphomas and sarcomas were identified as B lymphocyte tumors. They have surface immunoglobulin, Fc receptors, and Ia antigens. BIBLIOGRAPHIC REFERENCES: McMaster, Philip R. B., Owens, J. D. and Asofsky, R.: Hapten specific luekocyte migration inhibition. I. Inhibition of cells from animals immunized with DNP-KLH by epsilon-DNP-L-Lysine Ficoll. J. Immunol. 118: 1335-1337, 1977. McMaster, P. R. B., Owens, J . D., Dvorak, H. G., Weichbrod, R., and Asofsky, R.: Hapten specific delayed hypersensitivity to epsilon-DNP-L-Lysine-Ficoll in guinea pigs immunized with DNP-KLH. J. Exp. Med., 145: 1101-1114, 1977.